Despite improvements in economic and social standards in recent years, wide variations remain between the perinatal mortality rates of the countries of Europe (International Federations of Gynae-cology and of Midwives, 1966). Considerable variations also persist between the individual regions of England and Wales (Butler and Bonham, 1963). Within populations, low socio-economic status, short stature, advanced parity, and advanced age of mother (Duncan, Baird, and Thomson, 1952) are among the factors which increase the risk of peri-natal death. Standards of medical care, although not easy to measure, undoubtedly modify perinatal mortality (Baumgartner, 1962). These same factors may also be associated with low birth weight (Baird, 1964), and in England and Wales some 65 per cent. of the total of perinatal deaths occur in infants weighing less than 2,501 g. at birth. An analysis has been carried out to measure the extent to which variations in perinatal mortality between different parts of England and Wales are correlated with the distribution of birth weight. This analysis forms the first stage of a long-term study of the biology of low birth weight.

SOURCES OF MATERIAL The primary source of information for this study was the annual return, LHS 27/1, recording the total numbers of live and still births during 1963-65 in each local authority area in England and Wales. For infants in each birth weight group (1,000 g. or less, 1,001-1,500 g., 1,501-2,000 g., 2,001-2,250 g., and 2,251-2,500 g.) the numbers of live and still births, together with neonatal deaths within 24 hours of birth, within 1-6 days, and within 7-27 27